NUMERICAL INVESTIGATION OF A NEUTRAL HELIUM BEAM AS A DIAGNOSTIC PROBE IN THE PLASMA EDGES

We have made a simulation study of the interaction of a He neutral bea m and the JFT-2M tokamak plasma by using a set of coupled rate equatio ns. Our objective is to develop a spectroscopic diagnostic based on th e He neutral beam to study plasma parameters in the edge region of the tokamak plasma. One of the important issues is the spatial evolution of the metastable helium. Numerical results indicated that the He meta stable density was large enough for the measurements in the interactio n region, and that the several lower level populations (2(1)P, 3(1)D, etc.) were almost linearly proportional to the plasma density. Hence i t is possible to measure the plasma density by observing the emission line originating from the levels. We have also studied the forbidden e xcitation by a tunable laser (Stark effect) to measure the electric fi eld induced in the plasma edge region.